FR2623796A1 - Process for the manufacture of components of dual-composition propellent powder containing nitrocellulose and powder components thus obtained - Google Patents

Abstract

Process for the manufacture of components of dual-composition propellent powder containing nitrocellulose, in which the surface composition of the component is different from the composition at the core of the component. According to a preferred embodiment of the invention a component 5 made from a first propellent composition is wound onto a feed reel 4. This component 5 is caused to pass through a coating device 6 to be coated with a coating composition before moving into a sheathing enclosure 3. A second propellent composition placed in an extruder 1 fills the sheathing enclosure 3 where it is applied at an adjustable thickness around the component 5, which emerges in the form of a dual-composition component 7. The linear burning speed of the first composition is preferably higher than the linear burning speed of the second composition. The invention also relates to the dual-composition powder components thus obtained.

Description

Process for producing two-component propellent powder elements containing nitrocellulose and powder elements thus obtained
The present invention relates to the field of the manufacture of propellant powders, single base or multi-base, containing nitrocellulose intended in particular for artillery ammunition.

More specifically, the invention relates to a method of manufacturing two-composition propellant propellant powder containing nitrocellulose whose composition on the surface of the element is different from the composition in the core of the element. The invention also relates to the propellant powder elements obtained by the new process.

The most commonly used propellant propellant powders are nitrocellulose-containing powders, or nitrocellulose is the sole energy base for single-base powders, or nitrocellulose is used in admixture with other bases. energetic as by. for example, nitroguanidine, nitroguanidine, hexogen or polwinyl nitrate in the case of double or triple base powders.

A major problem to solve to improve the performance of the ammunition is that of the progressivity of the propellant charge. At the moment of ignition the powder starts to burn and the pressure rises in the socket of the ammunition. From a certain value, the projectile begins to be pushed into the barrel of the weapon which increases the volume available for the combustion gases. If the law of consumption of the powder (combustion rate and surface to be burned) remains constant, then a sudden drop in pressure is recorded, and thus a fall in the motive energy imparted to the projectile. It is therefore necessary to have powders whose law of consumption is not constant but increases during combustion to have an optimal effect on the projectile. To do this, the skilled person has two means. On the one hand it can play on the geometrical shape of each grain of propellant powder so that during combustion this grain develops a surface to be burned which is constant or even which increases. On the other hand it can play on the composition of each grain seeking to have grains of propellant powder whose surface composition has a lower linear velocity of combustion than that of the composition in the heart of the grain.

This is an old problem that was already tackled in 1913, for example in US Pat. No. 1,074,809. But if the question of having propellant powder elements whose surface composition is different from the internal composition is Although well covered in this patent, the means to achieve this are very vague and only a vague reference to a chemical modification of the surface composition of the powder element is noted. Later, those skilled in the art have been guided by developing the so-called "smoothing" technique, which consists, after manufacture of a powder element from a given propellant composition, in slowing down the superficial combustion rate of this element by superficial impregnation of a moderator of combustion such as camphor or centrality. This technique has been described, for example, in the book "Powder and explosives" by MM. L. VENIN,
E. BURLOT and H.LECORCHE, published in the Polytechnic Bookstore
Ch. Beranqer in 1932, p. 599-601, and continues to be the subject of recent research as for example the filing of the French patent application 2,385,661 issued in 1978 and-which relates to smoothing by means of esters or dinitriles of dicarboxylic acids aliphatic.

Nevertheless, the smoothing technique that relies on penetrating the surface by means of a solvent of a combustion moderator compound has the disadvantage of not allowing the man to perform a perfect control of both the depth of the and on the other hand the precise chemical composition of the moderate surface layer which usually exhibits a heterogeneous composition due to uneven penetration of the moderator compound. If the technique of lissaqe does indeed improve the progressiveness of the load, it does not allow a perfect control of all its parameters at the industrial Drocédés scale.

The object of the present invention is precisely to offer the skilled person a simple process that allows him to dispose of propellent powder bodies containing nitrocellulose consisting of a homogeneous internal composition and a homogeneous surface composition whose respective thicknesses are perfectly controllable without technological limitations.

To this end, the invention therefore relates to a method for manufacturing two-composition propellant propellant powder containing nitrocellulose, characterized in that, from a first propellant composition containing nitrocellulose, a shaped element is produced. strand or strip and that this element is coated with an adhesive composition consisting of at least one nitrocellulose solvent and is coated with a second propellant composition containing nitrocellulose.

According to a first preferred embodiment of the invention, the coating of the element constituted by the first propellant com- position is carried out by sheathing this element with said second propellant composition.

According to a second preferred embodiment of the invention, the linear combustion rate of the first composition is greater than the linear combustion rate of the second composition.

The invention also relates, as products, to the bi-composition propellent powder elements obtained by the process according to the invention.

By granular cutting of the bicomponent propellant powder elements obtained according to the invention, those skilled in the art possess progressive powder grains consisting of two distinct layers whose compositions and thicknesses are perfectly controlled and reproducible.

The following is a detailed description of the invention with reference to FIGS. 1 to 4.

Figure 1 shows schematically the implementation of the method according to the invention by means of a cladding plant.

Figure 2 shows a band-shaped bi-composition propellant powder element.

FIG. 3 represents a cylindrical strand bi-composition propellant powder element comprising a central channel.

FIG. 4 shows a cylindrical strand bi-shaped propellant powder element having seven channels.

FIG. 5 is a comparative diagram of the theoretical droughts of certain powders according to the invention and certain traditional casts.

The method according to the invention therefore consists in manufacturing, according to one of the techniques known to those skilled in the art, from a first propellant composition containing nitrocellulose a strand-like element or strip-like element, to coat this element with an adhesive composition consisting of at least one solvent of the nitrocellulose and coating the element thus coated with a second propellant composition containing nitrocellulose.

The solvent of the nitrocellulose used in said adhesive composition is preferably selected from the group consisting of acetone, ethyl alcohol, ethyl ether, ethyl acetate, triacetin and nitromethane. The amount of solvent used is left to the discretion of those skilled in the art but is generally between 0% and 1% by weight relative to the total weight of the two propellant compositions used.

In a preferred manner, the coating solvent is not used alone in the adhesive composition but in admixture with an additive selected from the group consisting of triacetin, ethylene glycol dimethacrylate, polyvinylidene chloride and polyvinyl chloride. polyethylene terephthalate.

It should be observed that in the context of the present invention triacetin may be used either as a solvent optionally in the presence of a separate additive, or as an additive, in this case necessarily in the presence of a separate solvent.

The presence of an additive in the adhesive composition is particularly advantageous in the case where said first composition contains a gelatinizing solvent for nitrocellulose such as nitroglycerine. In this case, the additive will limit the migration of nitroglycerine to the second composition used for coating. The weight ratio solvent / additive is generally between 1 and 20, advantageously close to 19 when the additive is polyvinylidene chloride or polyvinyl chloride and preferably close to 1 when the additive is triacetin used in the presence of a separate solvent.

The coating operations of the adhesive composition and of the embedding agent by the second propellant composition can be carried out in various ways: it is thus possible, for example, to proceed, for example, to the simultaneous extrusion in an extruder of the different compositions or to the simultaneous spinning with the Dresse des different compositions.

But as it has been observed by the Applicant that it is essential to obtain a bi-composition powder element having no gluing defects, that is to say without internal cracks between the two propellant compositions, that the powder element constituted by the first composition is coated with an adhesive composition before being coated with the second composition, the material realization of this coating by extrusion or spinning techniques poses problems of equipment that remove the At the present time these techniques are very much of their industrial interest. For reasons of industrial feasibility, the Applicant therefore recommends for an industrial implementation of the process a coating produced by a sheathing technique, also known to those skilled in the art. coating by the adhesive composition is then carried out separately before sheathing.

FIG. 1 shows the implementation of such a gain technique. FIG. 1 shows a screw extruder 1 comprising an extrusion head 2 emerging in a casing enclosure 3. On a reel 4 is wound the element 5 constituted from the first propellant composition, according to a conventional technique of spinning or extrusion.

This element 5 is passed through a coating device 6 before Dasser in the casing enclosure 3.

The coating device 6 may consist of, for example, a coating comb, a brush or any other equivalent device. The second propellant composition is placed in the extruder 1 through the feed funnel 12, pushed by the screw 11 it fills the enclosure of cladding 3 where it is applied to an adjustable thickness around the element 5 which emerges from the cladding enclosure 3 in the form of a bi-composition element 7 which comes for example to wind around a coil 8.

The element 5, the dimensions of which can be perfectly defined during its manufacture, must present the necessary flexibility for its implementation in a cladding technique which implies a quantity of residual solvents which is sufficient when this element is manufactured from a propellant composition with a single nitrocellulose base. Moreover, the outlet diameter of the cladding enclosure 3 being perfectly adjustable, a bi-composition element 7 is obtained, each composition of which is perfectly homogeneous and the thickness of each composition of which is perfectly defined.

Different external geometries can be used for the elements 5 and 7 and at the limit these geometries can be different from each other. However, in most cases, these geometries will be identical and usually the bicomposition element will be in the form of flat strips or strands having at least one central hole. In the latter case the strand will most generally look like a cylindrical strand.

FIGS. 2 to 4 show some forms of bi-composition propellant powder elements according to the invention.

In Figure 2 there is shown a member 20 in the form of a flat strip having a layer 21 consisting of a first propulsive composition and coated by a layer 22 constituted by a second propellant composition.

 FIG. 3 shows a cylindrical strand element 30 comprising a core 31 constituted by a first propulsive composition and coated by a layer 32 constituted by a second propulsive composition. The core 31 comprises a cylindrical central channel 33.

FIG. 4 shows a cylindrical strand element 40 comprising a core 41 constituted by a first propulsive composition and coated by a layer 42 constituted by a second propulsive composition. The core 41 comprises seven hollow cylindrical channels 43. This is an additional characteristic of the propulsive elements according to the invention: in multi-perforated cylindrical Doric geometry, the channels are all located in the central core formed by the first propulsive composition, since its shaping by conventional techniques allows the creation of channels, while the cladding technique is poorly suited to the establishment of hollow channels in the coating layer.

The said first and second compositions are propellant compositions containing nitrocellulose and more particularly compositions selected from the group consisting of compositions of propellants with nitrocellulose single base propellant with volatile solvent, propellant powders with double base containing nitrocellulose. and nitroglycerine, triple base propellant powders containing nitrocellulose, nitroglycerin, and a nitrated organic compound selected from the group consisting of hexogen, nitroguanidine, or polyvinyl nitrate.

As mentioned above, the first propellant composition constituting the friend of the two-component propellant element must contain sufficient volatile solvent or nonvolatile plasticizing element, depending on the type of composition, to present the necessary flexibility to its implementation in a cladding technique. Furthermore, according to a last preferred embodiment of the invention, the linear combustion rate of said first composition is greater than the linear combustion rate of the second composition. In the case of cylindrical geometries with a single central hole, the ratio of the thicknesses of each composition will be equal to the ratio of the linear combustion velocities of each composition.

The propellant powder element being thus manufactured, it is cut into grains which undergo any finishing treatment nitrocellulose propellant powders and especially the trem pages and drying to remove volatile solvents and soluble salts intended, after elimination to make the powder porous.

The skilled person thus has bi-composition powder particles particularly progressive as shown in Figure 5.

FIG. 5 shows a diagram comparing the theoretical progressivity of four powders.

The diagram represents, for each powder, its dynamic vivacity, that is to say the evolution of the mass surface S in combustion expressed in cm 2 / g as a function of the burnt depth P, that is to say of the advance different flame fronts in the grain of powder, expressed in mm.

Curve A is that of a nitrocellulose single-base powder, in the form of cylindrical grains with a single central channel, web 1.35 mm (web = thickness to be burned).

Curve B is that of a single-base nitrocellulose powder, in the form of cylindrical grains having 19 channels, web 1.34 mm.

Curve C is that of a powder according to the invention, in the form of cylindrical grains with a single central channel, web 1.50 mm whose internal composition is that of a single base powder nitrocellulose potential 980 calories per gram (4,100 J / g) and whose outer coating composition is that of a single base powder nitrocellulose potential 790 cal / g (3300 J / g).

Curve D is that of a powder according to the invention, in the form of single-channel central-globe grains of web 1.35 mm, the internal composition of which is that of a single base powder with nitrocellulose of potential 980 cal / g (4,100 J / g) and whose external coating composition is that of a nitrocellulose single base powder of potential 570 cal / g (2380 J / g).

From this comparative chart it is clear that
- a traditional monocomponent powder burns on the surface
constant in monotubular geometry (curve A) and
becomes really progressive in multitubu geometry
laire (curve B) but present in this. case an end of
degressive combustion,
a powder according to the invention is progressive already in geo
monotubular metrics (curves C and D) and, by choosing
well the constitutive compositions (curve D), can even
in monotubular geometry, be very definitely more pro
that a monocomponent multitubular
19 holes which is known as the most progressive of
traditional powders.

When it is known moreover that the greater the number of holes in a powder, Drus its apparent density decreases and correlatively the lower its loading coefficient, it will be appreciated that the invention allows the skilled person to have highly progressive propellant powders with a good loading coefficient.

The powders according to the invention thus find their preferential application in artillery ammunition.

The examples which follow illustrate certain possibilities of implementing the method according to the invention.

Example 1
Four types of cylindrical, monotubular powder strands were made.

Strands A: from a single base composition to nitro
cellulose (nitrogen content 12.5%) strands were made
0.7 mm web.

Strands B: from a composition 2 to a simple base with nitro
cellulose (nitrogen content 13.3%) strands were made
0.7 mm web.

Strands C: using composition 2 as internal composition
and the composition 1 as an external coating composition
0.7 mm Web strands were made by sheathing,
the thickness of the inner layer being 0.37 mm and
that of the outer coating layer being 0.33 mm.

It was not used for these strands of adhesive composition
sive.

Strands D: Strands similar to strands C were made, but
coating before sheathing the outer surface of the
inner layer by an adhesive composition
by a solution of 1 part of triacetin in 10 by
acetone.

The strands thus manufactured were shot in a pressure bomb at a loading density of 0.2 g / cm 3. The shooting results were as follows

<tb><SEP> Vivacity <SEP> dynamic
<tb><SEP> Gaseous <SEP> Flow <SEP> Mean <SEP> (Evolution <SEP> of <SEP><SEP> Surface <SEP> in
<tb><SEP> Strands <SEP> (in <SEP> meqa <SEP> Pascal <SEP> by <SEP> combustion <SEP> in <SEP> function <SEP> of
<tb><SEP> millisecond) <SEP> depth <SEP> burned)
<tb><SEP> A <SEP> 42 <SEP> degressive <SEP> of <SEP> order
<tb><SEP> l <SEP> 0 (<SEP> of <SEP> 50 <SEP>% <SEP> for <SEP> 80 <SEP>% <SEP> of
<tb> B <SEP> 51 <SEP> thickness <SEP> to <SEP> burn
<tb><SEP> regressive <SEP> of <SEP> the <SEP> order of
<tb><SEP> C <SEP> 107 <SEP> for <SEP> 80 <SEP>% <SEP> of <SEP> thickness
<tb><SEP> | <SEP> burn
<tb><SEP> slightly <SEP> progressive <SEP> of
<tb><SEP> D <SEP> 48 <SEP> the order <SEP> of <SEP> 8 <SEP>% <SEP> for <SEP> 80 <SEP>%
<tb><SEP> of <SEP> thickness <SEP> to <SEP> burn <SEP>
<Tb>
These results on the one hand confirm the theoretical diagram shown in Figure 5. For the same monotubular cylindrical geometry, the traditional strands A and B are decreasing while the strand D according to the invention is slightly progressive. Moreover, these results show the importance of the presence of an adhesive composition between the two nitrocellulose-based propellant compositions: the strand C which does not have a defect of internal cohesion which results in a very strong degression and a Abnormally high gas flow.

Exemole 2
From the reference monotubular cylindrical strands of outer diameter 3.01 mm, internal diameter 0.92 mm and Web 1.04 mm consisting of a nitrocellulose and nitroqlvcerine double base powder of potential 1 217 cal / (5,100 J / g) two sets of strands were manufactured according to the invention
Series A: gain coating with a double base composition
with nitrocellulose and nitroglycerine potential
804 cal / g (3,360 J / g) using triacetin
only as an adhesive composition (0.5% by mass
relative to the mass of powder).

Series B: identical coating but using as composition
Adhesive a 50/50 solution by mass of triacetin in acetone.

In both series the strands had the final dimensions
outer diameter: 4.50 mm
thickness of the adhesive layer: 0.15 mm.

The strands thus obtained were shot in a pressure bomb at a loading density of 0.2 g / cm 3. The performances were compared with those of the reference strands.

For lengths of 18.5 mm and 50 mm it has been observed that:
- reference strands burn degressively
aunt up to 80% of the thickness to be burned,
the strands of series A and B have a progressivity
constant evaluated at 12.12%, respectively up to 76%
the thickness to be burned for Series A and 80% of
the thickness to be burned for the series s.

Example 3
From monotubular cylindrical strands with a reference diameter of 3.1 mm, internal diameter 0.9 mm and web 1.04 mm, consisting of nitrocellulose and nitroglycerine double base powder of potential 1 217 cal / g (5,100 J / g) two series of strands were manufactured according to the invention:
Series A: cladding coating with a double base composition
with nitrocellulose and nitroglycerine potential
804 cal / q (3,360 J / g) using as composition
adhesive a triacetin solution containing 5%
mass of polyvinylidene chloride.

Series B: identical coating but using as composition
adhesive a solution of triacetin in acetone to
10% by weight of triacetin in the solution.

In both series the strands had the following final dimensions:
outside diameter: 4,50 isti
thickness of the adhesive layer: 0.04 mm.

The strands thus obtained were shot in a pressure bomb at a loading density of 0.2 g / cm 3. The performances were compared with those of the reference strands.

For lengths of 18.4 mm and 50 mm it was observed that:
- reference strands burn degressively
aunt valued at 15.9% up to 80% of the thickness at
burn,
- the strands of the series A burn with a progressivity
constant measured at 11.5% up to 72 th of the thickness at
burn for a raw manufacturing sample, we observe
Moreover this progressiveness is further improved
after an accelerated aging of 6 days at 70 ° C is
then 13.5% up to 80% of the thickness to be burned,
- the strands of the B series have a disintegrated combustion
sive from 50% up to 88% of the thickness to burn which
reveals a lack of cohesion between the two pro layers
associated with too low a triacetin
adhesive composition.

Example 4
The following powders were compared in combustion in a 105 mm artillery ammunition
- reference powders
monotubular cylindrical powder with a single nitro base
cellulose with a potential of 980 cal / g (4,100 J / g) and
2.4 mm web.

- powder A
monotubular cylindrical powder according to the invention:
- inner layer: single base nitro powder
cellulose with a potential of 980 cal / g (4,100 J / g),
67% porosity and 2.1mm web,
outer coating layer: single base powder
nitrocellulose with a potential of 980 cal / g
(4,100 J / g) and Web 0,7 mm,
adhesive composition: 50/50 solution by mass of
triacetin in acetone
- powder B
monotubular cylindrical powder according to the invention
- inner layer: single base nitro powder
cellulose with a potential of 980 cal / g (4,100 J / g),
100% porosity and web 2.4 mm,
outer coating layer: single base powder
nitrocellulose with a potential of 980 cal / g
t4 100 J / g) and web 0.6 mm,
adhesive composition: 50/50 solution by mass of
triacetin in acetone
For a maximum Dredge in the 435 MPa weapon we get

<tb><SEP> Powder <SEP> Load <SEP> of use <SEP> Speed <SEP> initial
<tb><SEP> of the <SEP> projectile
<tb> kg <SEP> 5.3kg <SEP> 1 <SEP><SEP> 470 <SEP>
<tb> C <SEP><SEP> 5.3 <SEP> ms <SEP>
<tb> A <SEP> 6 <SEP> kg <SEP> 1 <SEP> 550 <SEP> m / s
<tb> B <SEP> 5.3 <SEP> kg <SEP> k <SEP> 1 <SEP> 500 <SE> m / s <SEP> l <SEP>
<Tb>
These results show that for the same geometry the powders according to the invention lead to higher performance than conventional powders.

Example 5
In a similar manner to that of Example 4, we compared
- a cylindrical powder monotubular reference consti
killed by a nitrocellulose double base powder and
nitroglycerine potential of 1 250 cal / g (5200 J / g),
2.2 mm web,
a nonotubular eylinyl powder A according to the invention
- inner layer: nitro double base powder
cellulose and nitroglycerin potential
1250 cal / g (5200 J / g) and web 1.0 mm,
- external coating layer: double base coat with
nitrocellulose and nitroglycerin
potential 780 cal / g (3260 J / g) and web 0.5 mm,
adhesive composition: solution of triacetin and
of polyvinylidene chloride.

The following results were obtained

Powder <SEP> Load <SEP> of use <SEP> Speed <SEP> initial
<tb> Reference <SEP> 5.0 <SEP> kg <SEP> 1515 <SEP> m / s
<tb> A <SEP> 5.9 <SEP> kg <SEP> 1 <SEP> 570 <SE> m / s <SEP>
<Tb>
Example 6
In a similar manner to that of Example 4, we compared
- a reference powder with a single nitrocellulose base
in cylindrical grains with 19 channels and web
1.34 mm,
a monotubular cylindrical powder A according to the invention
- inner layer: nitro double base powder
cellulose and nitroglycerin potential
1250 cal / g (5200 J / g) and web 1.0 mm,
outer coating layer: single base powder
nitrocellulose with a potential of 760 cal / g
(3,180 J / g) and web 0.5 mm,
adhesive composition: 50/50 solution by mass of
triacetin in acetone
The following results were obtained

<tb> Powder <SEP> Load <SEP> of use <SEP> Speed <SEP> initial
<tb><SEP> of the <SEP> Projectile
<tb> Reference <SEP> 5,3 <SEP> kg <SEP> 1 <SEP> 525m / s <SEP>
<tb> A <SEP> 6.1 <SEP> kg <SEP> 1 <SEP> 570 <SEP> m / s
<Tb>
Examples 5 and 6 show that it is possible with the powders according to the invention to exceed the weapon performance of conventional single or double base powders, whatever their geometry.

Claims (10)

claims 1) A process for manufacturing two-component propellant propellant powders (20, 30) containing nitrocellulose, characterized in that a shaped element (21, 31) is produced from a first propellant composition containing nitrocellulose. in that it is coated with an adhesive composition consisting of at least one solvent of the nitrocellulose and is coated with a second propellant composition (22, 32) containing nitrocellulose. 2) Process according to claim 1 characterized in that said solvent is selected from the group consisting of acetone, ethyl alcohol, ethyl ether, ethyl acetate, triacetin and nitromethane. 3) Process according to any one of claims 1 or 2 characterized in that said solvent contains an additive selected from the group consisting of triacetin, ethylene glycol dimethacrylate, polyvinylidene chloride, polyvinyl chloride, polyethylene terephthalate. 4) Process according to claim 3 characterized in that the weight ratio solvent / additive is between 1 and 20. 5) Process according to any one of claims 1 to 4 characterized in that the coating of the element (5) consisting of the first propellant composition is produced by passing this element (5) in a casing enclosure (3 ) in which is supplied said second propellant composition. 6) Process according to any one of claims 1 to 5 characterized in that said bi-composition propellant powder element has the shape of a strand having. at least one central hole. 7) Method according to claim 6 characterized in that said strand is a cylindrical strand. 8) Process according to any one of claims 1 to 7 characterized in that said first composition and second composition are selected from the group consisting of propellant powders compositions with a single base with nitrocellulose with volatile solvent, propellant powders with nitrocellulose and nitroglycerin-containing double base, nitrocellulose-containing triple base propellant powders, nitroglycerin and a nitro organic compound selected from the group consisting of hexoqene, nitroguanidine and polyvinyl nitrate. 9) Process according to any one of claims 1 to 8 characterized in that the linear combustion rate of the first composition is greater than the linear combustion rate of the second composition. 10) Two-component propellant powder elements obtained by the process according to any one of claims 1 to 9.